1. Field of the Invention
The present invention relates to a voltage detecting apparatus that detects the voltage of a detected object and to a line voltage detecting apparatus equipped with such voltage detecting apparatus.
2. Description of the Related Art
As one example of this type of a voltage detecting apparatus, a non-contact voltage measuring apparatus (hereinafter, also referred to as a “voltage detecting apparatus”) disclosed by Japanese Examined Patent Application Publication H07-58297 is known. This voltage detecting apparatus is a non-contact potential measuring apparatus that reads changes in potential of a detected object (or “sample”) in a non-contact manner, and includes a metal prong with a pointed end, a feedback circuit that detects a field emission current or tunnel current via the metal prong and applies a voltage to the metal prong so as to keep such current constant, and a circuit that reads the voltage of the metal prong. With this voltage detecting apparatus, when the metal prong is held near the detected object, the feedback circuit carries out control over the voltage applied to the metal prong so as to keep the field emission current or tunnel current constant. Since the voltage of the metal prong at this time will follow the voltage of the detected object, by reading the voltage of the metal prong, it is possible to read (i.e., detect) changes in the voltage of the detected object. This voltage detecting apparatus is constructed using a current-to-voltage converter as part of the feedback circuit and converts the field emission current or tunnel current to a voltage signal using the current-to-voltage converter.